In this file photo, workers install signage in preparation for Super Bowl XLVII which was held February 3, 2013 at the Mercedes-Benz Superdome.

NEW YORK — The San Francisco 49ers and the Baltimore Ravens won their National Football League championships in stunning fashion on Sunday to set up an extraordinary sibling rivalry in next month's 47th Super Bowl.

The 49ers, coached by Jim Harbaugh, overturned a 17 point deficit to beat the Atlanta falcons 28-24 in the NFC decider before the Ravens, under the guidance of Jim's older brother John, stunned the highly-fancied New England Patriots 28-13 in the AFC title game.

Sibling rivalries are not uncommon in sport, most notably with the Williams sisters in tennis, but it will be the first time that head coaches from the same family square off for the greatest prize in American professional sports.

"I don't know if we had a dream this big," John Harbaugh told reporters.

With a bit more luck, the pair might have met in the Super Bowl last year but both came up short with the 49ers losing the NFC championship in overtime to the New York Giants and the Ravens losing by three points to the Patriots in the AFC.

This time, both teams ended up on the winning end of the scoreboard to book their places at the Superdome in New Orleans on Feb. 3.

The 49ers, one of American Football's most successful franchises, will be making their first appearance in the Super Bowl for 18 years.

They have never lost an NFL title game and if they maintain their perfect record they will tie the Pittsburgh Steelers' record of six titles.

Their chances of just getting to the Super Bowl looked doomed after they fell 17-0 down in the early second quarter, a deficit no team had ever overcome in the NFC championship game.

With second year quarterback Colin Kaepernick calling the shots, they rallied back with two touchdowns, briefly cutting the margin to three points before Atlanta quarterback Matt Ryan connected with retiring tight end Tony Gonzalez to give the Falcons a 10-point advantage at halftime.

But the Falcons failed to score a single point in the second half while San Francisco running back Frank Gore scored two unanswered touchdowns to secure his team's victory.

"We are tough, it is hard to break us. We aren't going to give up," Gore said. "We will keep fighting into the fourth quarter and until the game (clock) hits double zero."

IRRESISTIBLE DISPLAY

It was a bitter loss for the Falcons, who finished the regular season with the best record in the NFL to secure the home-field advantage for the playoffs, but they had no excuses.

"We didn't make the plays when we had the opportunities," Falcoms head coach Mike Smith said. "There were ebbs and flows and changes in momentum and they made more plays then we did."

Baltimore, riding high on a wave of emotion and inspiration from their veteran linebacker Ray Lewis, outscored the Pats 21-0 in a lopsided second half to reach the Super Bowl for just the second time.

Given little hope of beating a New England team led by Tom Brady, they avenged their loss to the Pats in the corresponding game last year after an irresistible display by underrated quarterback Joe Flacco.

"I said to our players last year, don't put your heads down, we'll be back," said Lewis, a 13-time Pro Bowler who is retiring after the Super Bowl.

"To see us come back like this, after all the injuries and things we have been through... our team is just awesome and this our time."

For New England, the most dominant team in the NFL over the past decade and a half, it was another case of so close but yet so far.

Despite winning three titles between the 2001 and 2004 seasons, the Pats lost their last two Super Bowl appearances, including last season, in agonising fashion.

You have the opportunity to win the game and we came up short," Brady lamented. "There's frustration in that we wish we could have done better." (Editing by John O'Brien)